TABLE 26 - Stability, Overturning Seaward 



Forces 



Arm (from B) 

 (feet) 



Moment about B 

 (ft. -lbs. per ft.) 



(lbs, per ft.) 



Concrete (Vertical) 2U,500 



Earth (Vertical) 8,hOO 



Earth (Horizontal) 13,950 



Uplift (Vertical) 12,8UO 



TOTAL 



NET TOTAL 



12,18 



17.65 



7.8U 



13.33 



+109,000 

 +171,000 



-298,000 



"lUSjOoo 



+280^000 -Uj.6,000 

 -166 J 000 



The moments which would cause overturning around point B are positive, 

 therefore the wall is stable under saturated earth forces, 



285. Internal Stresses. - Overturning Landward . ~ Although the wall 

 is stable against overturning, calculation of the resultant of the forces 

 indicates that this resultant would fall outside the middle third of the 

 base. The total vertical force of 32,280 t)o\inds per foot downward would 

 be applied 7,16 feet from A, The to tax horizontal force, which would be 

 16,870 pounds per foot directed landward, would be applied 11,5 feet above 

 the base» From Figure 96, the resultant of these forces would fall 1.1 

 feet from A inside the base. 



286. It would be possible, by adding to the area of concrete to 

 bring the resultant of the forces within the middle third, or at least to 

 reduce the tension in the base. However, because of the high dynamic 

 pressures of the breaking waves, to eliminate . tension completely (or even 

 to materially r educe the tension) would require an excessively large amount 

 of additional concrete. Accordingly the economics of providing the 

 additional concrete as opposed to the provision of tension steel must be 

 weighed locally. No such analysis will be made for the purpose of design 

 illustration. It should alao be noted that tension steel for the given 

 design will be required in the front face of the wall. 



287. Foundation Pressures. - Overturning Landward . - The bearing 

 pressure of the loads may be calculated from 



^ A - Z 



where P « sum of vertical loads = 32,280 



A = base area (unit length of wall) = 20 



M = the total moment about the base centerline 



= 16,870 X 11.5 + 32,280(10-7.16) ^ 287,000 20^ 

 3 = the section modulus (unit length of wall) » — r— 



Therefore f = 32,280 + 6 x 287,000. 

 20 - HOO^ 



* 1600 + U300 



li;l 



(69) 



